How to import logsumexp from keras.backend?

Question

To be able to use logsumexp in the keras.backend, what is the appropriate way to import Keras 2?

Here is what I have tried and failed in colab. Both get AttributeError: module 'keras.backend' has no attribute 'logsumexp'

• 1st round:

    import tensorflow
    import keras
    import keras.backend as K

    K.logsumexp
    keras.__version__ # 2.15.0
    tensorflow.__version__ #2.15.0

• 2nd round with a new session

    import tensorflow
    from tensorflow import keras
    from keras import backend as K

    K.logsumexp
    tensorflow.__version__ #2.15.0

I doubt the reason is that logsumexp is not decorated as others in keras.backends.

@keras_export('keras.backend.logsumexp')
@dispatch.add_dispatch_support